How to Open and Read a HAR File

A HAR file is a record of everything your browser sent and received during a web session

A HAR file (HTTP Archive) is a text file that logs every request your browser made and every response it got back while you were loading a website. It captures the URLs, headers, cookies, response times, file sizes, and content of each request — everything a web developer needs to see what happened under the hood. You cannot open it like a regular document; you need either a text editor to read the raw data, or a tool that formats it into something human-readable.

HAR files are usually created when you record a browser session using the Network tab in your browser's developer tools, then export that recording. They are plain text files written in JSON format, so they are portable — you can send them to another developer, open them on a different computer, or analyze them with specialized tools.

Key Takeaways

A HAR file is a JSON text file that records all the HTTP requests and responses from a browser session, created by exporting data from the Network tab in developer tools.
You can open a HAR file in any text editor (Notepad, VS Code, Sublime Text) to see the raw JSON, but the data is dense and hard to read without formatting.
Online HAR viewers and dedicated tools like HAR Analyzer, Fiddler, or Charles Proxy format the data into readable tables and charts that show load times, file sizes, and request details.
The fastest way to view a HAR file is to drag it into your browser's Network tab or use a free online viewer like toolbox.googleapps.com/apps/har_analyzer/.

Opening a HAR file in a text editor

The simplest way to open a HAR file is to right-click it, choose "Open with", and select any text editor — Notepad on Windows, TextEdit on Mac, or VS Code, Sublime Text, or Atom if you have them installed. The file will open as plain text showing the raw JSON data.

This approach works, but the output is hard to scan. A HAR file for even a straightforward page load can be hundreds of lines long, with nested brackets and quotation marks everywhere. You will see entries like "startedDateTime": "2024-01-15T14:32:18.450Z" and "timings": {"blocked": 5, "dns": 12, "connect": 45}, but finding the information you actually need takes scrolling and searching.

Use a text editor only if you need to search for a specific URL, domain, or header value, or if you want to remove sensitive data (like authentication tokens or personal information) before sharing the file with someone else.

Viewing a HAR file in your browser's developer tools

The fastest way to view a HAR file in a readable format is to open your browser's developer tools, go to the Network tab, and drag the HAR file directly into it. Chrome, Firefox, and Edge all support this.

In Chrome: open developer tools (F12 or right-click → Inspect), click the Network tab, then drag the HAR file onto the tab. The requests will populate the Network panel as if you had just recorded them. You can then click any request to see its headers, response, cookies, and timing details — all formatted and clickable instead of buried in JSON.

In Firefox: open developer tools, go to the Network tab, click the settings icon (gear), scroll down to "Import HAR", and select your file. The requests appear in the same organized list.

Using online HAR viewers

If you do not want to open developer tools, several free online tools will parse a HAR file and display it as a formatted report. Google's HAR Analyzer (toolbox.googleapps.com/apps/har_analyzer/) is the most widely used. Upload your HAR file and it shows a waterfall chart of all requests, sorted by domain, with load times color-coded and file sizes listed.

Other options include Har Viewer (ericduran.github.io/chromeHAR/), which displays requests in a collapsible tree, and Fiddler's online HAR viewer. These tools are useful if you are sharing the file with a non-technical person or if you want a quick visual summary without opening developer tools.

Be aware that uploading a HAR file to an online tool means sending the file's contents to that website's server. If the HAR file contains sensitive information — authentication tokens, API keys, personal data, or internal URLs — either remove that data first (by editing the JSON in a text editor) or use a local tool instead.

Using desktop tools like Fiddler or Charles Proxy

If you work with HAR files regularly, desktop applications like Fiddler (fiddler2.com) or Charles Proxy (charlesproxy.com) let you open and inspect HAR files alongside live traffic capture. Both are free or low-cost and give you more control than online viewers.

Fiddler: go to File → Open Archive → Open HAR File, select your file, and the requests appear in Fiddler's main window. You can filter by domain, search for specific headers, and export subsets of the data.

Charles Proxy: go to File → Open HAR, select your file, and it loads into the session list. Charles is particularly useful if you need to modify requests or responses and re-export the HAR file.

These tools are overkill for a one-time look at a HAR file, but they are worth learning if you are debugging performance issues or analyzing traffic patterns across multiple sessions.

What to look for in a HAR file

Once you have the file open in a readable format, focus on a few key columns: the request URL, the HTTP status code (200 means success, 404 means not found, 500 means server error), the file size, and the time taken. A waterfall view shows you which requests blocked others — if a large JavaScript file took 5 seconds to read, everything that depended on it had to wait.

Look for failed requests (status codes in the 400s or 500s), unusually large files, or requests to unexpected domains. If a page is slow, the HAR file will show you whether the problem is a slow server response, a large read, or the browser waiting for something else to finish first.

The "timings" section for each request breaks down the delay into stages: DNS lookup, TCP connection, TLS handshake (if HTTPS), waiting for the server to respond, and downloading the response. This tells you whether the slowness is a network problem, a server problem, or a browser rendering problem.

Removing sensitive data before sharing a HAR file

HAR files often contain information you do not want to share: session cookies, authentication tokens, API keys, personal information in URLs or response bodies, or internal server names. Before sending a HAR file to a developer outside your organization, open it in a text editor and search for and remove these values.

Look for entries like "Set-Cookie", "Authorization", "X-API-Key", or any header containing a token or secret. Also check the response bodies — if a request returned JSON with user data or database IDs, delete or redact that too. Save the edited file and send that version instead.

Some tools like Fiddler have built-in options to mask sensitive headers when exporting, but manual review is safer.

Frequently Asked Questions

Can I create a HAR file myself, or do I need a developer to send it to me?

You can create one yourself. Open your browser's developer tools (F12), go to the Network tab, reload the page or perform the actions you want to record, then right-click in the Network panel and select "Save all as HAR with content" (Chrome) or "Save as HAR" (Firefox). The file downloads to your computer.

What is the difference between a HAR file and a screenshot?

A screenshot shows what the page looked like at one moment. A HAR file shows every request the browser made to build that page — the URLs, response times, file sizes, and headers. A developer can use a HAR file to diagnose why a page is slow or why something failed to load, but a screenshot cannot tell them that.

Is it safe to open a HAR file someone sent me?

Opening a HAR file in a text editor or your browser's developer tools is safe — it is just data. Uploading it to an online tool is safe only if you trust that website and the file does not contain secrets. If you are unsure, open it locally in a text editor or your browser instead.

Why is my HAR file so large?

HAR files include the full content of every response — images, videos, and large JSON responses are stored in their entirety. A page that loads 50 images will produce a large HAR file. You can reduce the size by recording only the requests you care about, or by opening the file in a text editor and deleting the response bodies you do not need.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.